The invention relates to a method for the early induction of an additional start of an internal combustion engine in a vehicle with a hybrid drive.
At the present time there already exist a wide variety of designs of vehicles with a hybrid drive for reducing emissions and fuel consumption. In these designs the hybrid drive consists of at least one electric drive unit and an internal combustion engine. In this case the determined nominal drive torque is split between the two drive units as a function of the current operating conditions of the vehicle so that the vehicle can be operated in a consumption optimized and/or emissions optimized operating mode.
Since in conventional actuation systems the electric drive unit can implement requested load changes significantly faster than an internal combustion engine, there already exist a plethora of methods for achieving just as fast an implementation of the torque requests given to internal combustion engines, in order to enhance the driving comfort. Hence, DE 10 2005 060 858 A1 discloses a method for operating a hybrid vehicle. According to this method, the unfiltered cumulative nominal torque is used as the basis for the division among the different drive units, so that the division yields a lead nominal torque for the slower path of an internal combustion engine. In this way higher driving dynamics are achieved. This method is designed especially for improving the dynamics when both drive units are in operation or at least the internal combustion engine is in operation. A strategy for the case, in which only the electric drive unit is in operation, is neither disclosed nor suggested.
When only the electric drive unit is in operation, the prior art does not generally activate the internal combustion engine until the nominal drive torque of the electric drive unit, or more specifically, the determined total nominal drive torque (since only the electric drive unit is active), exceeds the maximum possible available drive torque of the electric drive unit.
For a better understanding of the invention, the prior art method is shown in FIG. 1. According to the prior art, the torque requested by the driver Mdk_request is determined as a function of the position of the accelerator pedal sFP in that the position of the accelerator pedal influences the scaling specified by the maximum possible total torque of the drive train. That is, an interpretation of the accelerator pedal is performed. If the minimum total drive torque is, for example, −80 Nm, and the maximum total drive torque is 420 Nm, then a 20% actuation of the accelerator pedal is equivalent to a driver request torque Mdk_request of 100 Nm. However, the driver request torque Mdk_request cannot be set immediately for comfort reasons (for example, drive train vibrations). For this reason, the driver request torque Mdk_request runs through a driving dynamics filtering. At this point the driver request torque that is filtered with respect to the driving dynamics still has to run through torque coordination in order to be able to consider the external and internal requesters, that is, the external and internal requested torque limits (for example, operation under emergency conditions) and/or external torque intervention (for example, gear shifts, DSC intervention) when the nominal drive torque is specified. After the torque coordination the result is a (total) nominal drive torque Mdk_nominal, which is used within the framework of the torque splitting for splitting the nominal drive torque Mdk_nominal between the electric drive unit and the internal combustion engine.
When only the electric drive unit is in operation, the (total) nominal drive torque Mdk_nominal is demanded only of the electric drive unit. Not until the actuator unit of the electric drive unit detects that this electric drive unit cannot achieve and/or provide the requested nominal drive torque Mdk_nominal is an additional startup of the internal combustion engine requested. The result is a response loss, because initially the drive system lacks the necessary accelerating torque.
The object of the invention is to provide a method in which no unnecessary response losses occur when only the electric drive unit is in operation and an additional startup of the internal combustion engine is necessary.
This engineering object is achieved by a method for the early induction of an additional start of an internal combustion engine in a vehicle with a hybrid drive comprising at least one electric drive unit and one internal combustion engine, wherein when only the electric drive is in operation, then the internal combustion engine is additionally started no later than when the determined requested nominal drive torque exceeds the maximum possible drive torque of the electric drive unit. The requested nominal drive torque is determined as a function of the determined filtered driver request torque. In order to initiate an additional startup of the internal combustion engine before reaching or exceeding the maximum possible drive torque of the electric drive unit by means of the requested nominal drive torque, the still unfiltered driver request torque or a limited driver request torque is evaluated.
An aspect of the invention is to predict in real-time the (total) nominal drive torque or, more specifically, the nominal drive torque of the electric drive unit, so that an additional startup of the internal combustion engine can be initiated very early. In order to be able to predict the nominal drive torque of the electric drive unit or more specifically the (total) nominal drive torque, the determined driver request torque is already used and evaluated before consideration of all driving dynamics filters.
The inventive method for early induction of an additional start of an internal combustion engine in a vehicle with a hybrid drive including at least one electric drive unit and one internal combustion engine, provides, in principle, the internal combustion engine to be additionally started when the nominal drive torque, which is determined from the filtered driver request torque, reaches or exceeds the maximum possible drive torque of the electric drive unit at this time. In order to initiate the additional startup of the internal combustion engine already before reaching or exceeding the maximum possible drive torque of the electric drive unit, the still unfiltered driver request torque or a limited driver request torque is evaluated. By evaluating the unfiltered driver request torque an early prediction of the (total) nominal drive torque is possible and, in so doing, it is possible to quickly initiate measures for activating the internal combustion engine.
The maximum possible and/or available drive torque of the electric drive unit is specified at least as a function of the charge state of a battery unit, which supplies the electric drive unit with energy, and/or as a function of the operating temperature of the battery unit. In addition, it is also possible to consider other relevant parameters.
The determined unfiltered driver request torque is evaluated advantageously in such a way that this driver request torque or a driver request torque that is limited due to the presence of permanent torque limiters is compared with the maximum possible drive torque of the electric drive unit. If the unfiltered driver request torque or the limited driver request torque reaches or exceeds the maximum possible drive torque of the electric drive unit, then measures for an additional startup of the internal combustion engine are initiated.
In order to prevent the internal combustion engine from starting up too early, an advantageous embodiment of the invention provides that on reaching or exceeding the maximum possible drive torque of the electric drive unit by means of the determined driver request torque or the limited driver request torque, the measures for the additional startup of the internal combustion engine can be blocked or can be carried out only after a time delay. In particular, the measures can be blocked or carried out with a time delay, when the conditions for blocking or delaying are present or rather are fulfilled. The conditions for blocking or delaying may be met, for example, when, based on the current operating conditions, the external and/or internal power requesters request that the driver request torque be limited for at least a specified period of time.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.